This invention relates to improvements in electronic private automatic branch exchanges (EPABX's) for controlling telephone calls.
PBX's, which include EPABX's, may be completely automatic, but many are manned by an attendant, during normal work hours, at least. In those places not requiring a PBX attendant during all hours, it is still desirable that persons in the area served by the PBX during the hours that the PBX is unattended be able to complete outgoing and incoming calls. Outgoing calls are usually made by dialing one or two predetermined digits from a telephone station to cause the PBX control circuits and registers to connect the calling station to an outgoing trunk line to the telephone company's central office.
Incoming calls are, on the other hand, more difficult to handle. Usually, provisions are made at the PBX control console to connect each incoming trunk to a specific telephone station. When an incoming call is received, telephone station associated with that trunk rings and the incoming call must be taken at that station. This arrangement is often unsatisfactory because the station connected to the trunk may be remote from the location in which persons might be located. Call pick-up services have a similar disadvantage.
Another disadvantage of the prior art circuits for receiving incoming calls through an unattended PBX with incoming trunks patched to specific stations is that the stations so patched can only make outgoing calls or receive incoming ones. They cannot be used to call other stations within the same PBX system.
The described disadvantages can be overcome by using a Universal Night Answering (UNA) or Assigned Night Answering (ANA) circuit as described herein.